論理演算子
I thought string operators were for use with strings or strings and numbers. But that is incorrect. You can use the '.' operator to concatenate two numbers, as follows:
echo 1 . 2;
I assume that behind the scenes the 1 and 2 are converted to strings to allow the concatenation. What triggers the conversion? I'll guess the dot operator.
文字列演算子
文字列の演算子は 2 種類あります。最初のは結合演算子('.')で、右引数と 左引数を結合したものを返します。2 番目は、結合代入演算子('.=')で、 この演算子は右側の引数に左側の引数を追加します。詳細は、代入演算子 を 参照ください。
<?php
$a = "Hello ";
$b = $a . "World!"; // $b は、"Hello World!" となります。
$a = "Hello ";
$a .= "World!"; // $a は、"Hello World!" となります。
?>
add a note
User Contributed Notes文字列演算子
mehea
20-May-2008 09:31
20-May-2008 09:31
kevin at metalaxe dot com
10-Nov-2006 11:57
10-Nov-2006 11:57
I ran the follow script and found that using "$var" was 'mostly' slower than using ' '.$var
<?php
$var = 1;
for( $x=0; $x < 101; $x++ )
{
echo '<br /><br />var = int( '.$var.' )<br />';
$timer->reset();
for( $i=0; $i<100001; $i++ )
{
$string = " {$var} {$var} {$var} {$var} {$var} {$var} {$var} {$var} {$var} {$var} {$var} {$var} {$var} {$var} {$var}";
unset( $string );
}
echo 'One string with 15 $vars was set using one concat 100000 times and took '.$timer->fetch_time().' seconds to execute <br />';
$timer->reset();
for( $i=0; $i<100001; $i++ )
{
$string = ' '.$var.' '.$var.' '.$var.' '.$var.' '.$var.' '.$var.' '.$var.' '.$var.' '.$var.' '.$var.' '.$var.' '.$var.' '.$var.' '.$var.' '.$var;
unset( $string );
}
echo 'One string with 15 instances of $var was set using multiple concats 100000 times and took '.$timer->fetch_time().' seconds to execute';
}
exit();
?>
Replacing $timer with a generic timing class of course.
caliban at darklock dot com
30-Mar-2006 04:10
30-Mar-2006 04:10
WRT Stephen's note:
My example of concatenation and array methods of string building does not include the interstitial logic, which is expected to include conditionals.
Concatenation method:
$str="This is my list";
if($list=="o") $str.="<ol>";
else $str.="<ul>";
foreach($item as $i) $str.="<li>$i</li>";
if($list=="o") $str.="</ol>";
else $str.="</ul>";
Array method:
$str=array("This is my list");
if($list=="o") $str[]="<ol>";
else $str[]="<ul>";
foreach($item as $i) $str[]="<li>$i</li>";
if($list=="o") $str[]="</ol>";
else $str[]="</ul>";
$str=implode("",$str);
You can't do either of these with a single double-quoted string. However, if what you are doing CAN be done in a single double-quoted string, Stephen is completely correct in observing that you should do that instead of concatenating.
Stephen Clay
24-Dec-2005 12:10
24-Dec-2005 12:10
<?php
"{$str1}{$str2}{$str3}"; // one concat = fast
$str1. $str2. $str3; // two concats = slow
?>
Use double quotes to concat more than two strings instead of multiple '.' operators. PHP is forced to re-concatenate with every '.' operator.
caliban at darklock dot com
16-Dec-2004 12:57
16-Dec-2004 12:57
String concatenation is faster than the array method:
$str="";
$str.="Some string";
$str.="Some other string";
...
$str.="The last string";
That runs roughly twice as fast as:
$str=array();
$str[]="Some string";
$str[]="Some other string";
...
$str[]="The last string";
$str=implode("",$str);
Not that I think this is a terribly widespread practice, but I've got an awful lot of legacy code with this array method in it and a comment to the effect that it's faster than string concatenation. Testing has shown the exact opposite, so I figured I'd enlighten anyone else with this misconception.
anders dot benke at telia dot com
28-Apr-2004 01:53
28-Apr-2004 01:53
A word of caution - the dot operator has the same precedence as + and -, which can yield unexpected results.
Example:
<php
$var = 3;
echo "Result: " . $var + 3;
?>
The above will print out "3" instead of "Result: 6", since first the string "Result3" is created and this is then added to 3 yielding 3, non-empty non-numeric strings being converted to 0.
To print "Result: 6", use parantheses to alter precedence:
<php
$var = 3;
echo "Result: " . ($var + 3);
?>
php dot net at rinner dot at
20-Feb-2001 10:00
20-Feb-2001 10:00
Also see http://www.php.net/manual/en/language.types.string.php for usage of here doc syntax ("<<<")